1. Field of the Invention
The present invention pertains to cellular telecommunications, and particularly to congestion control in a mobile telecommunications system.
2. Related Art and Other Considerations
In mobile telecommunications, a mobile station (MS) such as mobile telephone communicates over radio channels with base stations. Each base station usually transmits and receives signals over selected radio channels for a particular geographic region known as a cell. The cell often is subdivided into several sectors. Typically a plurality of base stations are connected to a base station controller node, also known as an exchange or a radio network controller node (RNC). One or more RNCs are, in turn, connected to or included with a mobile switching center (MSC). The mobile switching center is usually connected, e.g., via a gateway, to other telecommunication networks, such as the public switched telephone network or to a packet-data network such as the Internet.
FIG. 1 shows a radio access network (RAN) 20 which comprises radio network controllers (RNC) 22.sub.1 and 22.sub.2 respectively connected to mobile switching centers (MSC) 24.sub.1 and 24.sub.2. Radio network controller (RNC) 22.sub.1 is connected to base stations (BS) 26.sub.1,1, 26.sub.1,2, and 26.sub.1,3 ; radio network controller (RNC) 22.sub.2 is connected to base stations (BS) 26.sub.2,1, 26.sub.2,2, and 26.sub.2,3. The radio network controllers (RNC) 22.sub.1 and 22.sub.2 are connected by an inter-RNC transport link 32.
In a code division multiple access (CDMA) mobile telecommunications system, the information transmitted between a base station and a particular mobile station is modulated by a mathematical code (such as spreading code) to distinguish it from information for other mobile stations which are utilizing the same radio frequency. Thus, in CDMA, the individual radio links are discriminated on the basis of codes. Various aspects of CDMA are set forth in Garg, Vijay K. et al., Applications of CDMA in Wireless/Personal Communications, Prentice Hall (1997).
In addition, in CDMA mobile communications, typically the same baseband signal with suitable spreading is sent from several base stations with overlapping coverage. The mobile terminal can thus receive and use signals from several base stations simultaneously. Moreover, since the radio environment changes rapidly, a mobile station likely has radio channels to several base stations at the same moment, e.g., so that the mobile station can select the best channel and, if necessary, use signals directed to the mobile from various base stations in order to keep radio interference low and capacity high. This utilization of radio channels to/from multiple base stations by a mobile station, such as occurs in a CDMA scheme for example, is termed "soft handover" or "macro diversity."
At the moment shown in FIG. 1, and for reasons summarized above, mobile station MS is shown in FIG. 1 as having radio communication with two base stations, particularly base stations 26.sub.1,2, and 26.sub.1,3. The lines 28.sub.1,2 and 28.sub.1,3 each represent a communication path. Specifically, line 28.sub.1,2 depicts both the radio channel from mobile station MS to base station BS 26.sub.1,2 and the land line link channel from base station BS 26.sub.1,2 to radio network controller (RNC) 22.sub.1 ; line 28.sub.1,3 depicts both the radio channel from mobile station MS to base station BS 26.sub.1,3 and the land line link channel from base station BS 26.sub.1,2 to radio network controller (RNC) 22.sub.1. In the case of both lines 28.sub.1,2 and 28.sub.1,3, the land line link is connected to a diversity handover unit (DHU) 30.sub.1 of radio network controller (RNC) 22.sub.1.
Thus, as depicted with reference to FIG. 1, the mobile connection with mobile station MS potentially utilizes several "legs", each leg being represented by the lines 28.sub.1,2 and 28.sub.1,3 in the case of mobile station MS of FIG. 1. As the overall connection between mobile station MS and any other party is viewed, the diversity handover unit (DHU) 30.sub.1 serves essentially both to combine and split the different legs utilized by a mobile station. The splitting occurs in the sense that information directed toward the mobile station is directed along the plural parallel legs to differing base stations. Information received from a base station may actually be obtained through several of the legs (e.g., from several base stations), in which sense the diversity handover unit (DHU) 30.sub.1 serves a combining function. Operations performed by a diversity handover unit are understood, for example, with reference to copending U.S. patent applications Ser. No. 08/979,866, filed Nov. 26, 1997 and entitled "MULTISTAGE DIVERSITY HANDLING FOR CDMA MOBILE TELECOMMUNICATIONS", which is incorporated herein by reference.
FIG. 1 illustrates the simple case in which the different legs of the connection, represented by lines 28.sub.1,2 and 28.sub.1,3, are for base stations BS all of which are connected to radio network controller (RNC) 22.sub.1. However, should the mobile station MS travel sufficiently to pick up signals from another base station, e.g., into or proximate a cell handled by another base station, such as base station BS 26.sub.2,1, for example, a more complex situation occurs as shown in FIG. 1A.
The situation depicted in FIG. 1A introduces the concept of a border 31 between groups of cells controlled by base stations which are, in turn, controlled by different RNCs. In FIG. 1A, the mobile station MS communicates not only through the leg represented by line 28.sub.1,3, but now also by the leg represented by line 28.sub.2,1. The leg represented by line 28.sub.2,1 includes the radio link between mobile station MS and base station BS 26.sub.2,1, as well as the information pertinent to the mobile connection which is carried over inter-RNC transport link 32.
Thus, in the situation depicted in FIG. 1A, the mobile connection involving mobile station MS employs base stations belonging to differing radio network controllers (RNC). Such situation involves a different type of handover--an inter-RNC soft handover. Inter-RNC soft-handovers are made between two or several RNCs. In the particular situation shown in FIG. 1A, an inter-RNC soft handover is made between radio network controller (RNC) 22.sub.1, which is also known as the "Source" RNC, and radio network controller (RNC) 22.sub.2, which is also known as the "Target" RNC. Radio network controller (RNC) 22.sub.1 is the Source RNC since it has current control of the mobile radio connection. The Target RNC is an RNC, other than the Source RNC, that has, or has been decided to have, base stations utilized by the mobile radio connection.
The inter-RNC transport link 32 which connects the radio network controllers (RNC) 22.sub.1 and 22.sub.2 facilitates, e.g., the inter-RNC soft-handovers. Inter-RNC transport link 32 is utilized for the transport of control and data signals between Source RNC 22.sub.1 and Target RNC 22.sub.2, and can be either a direct link or a logical link as described, for example, in International Application Number PCT/US94/12419 (International Publication Number WO 95/15665).
International Application Number PCT/FI94/00038 (International Publication Number WO 95/20865) involves border base stations that are connection to two RNCs. When the mobile station becomes connected to at least one border base station, but no base station owned by the source RNC, the inter-RNC handover can occur.
There are inter-exchange handover protocols specified such as GSM Recommendation 09.02 "Mobile Application Part (MAP)" for GSM; IS41 for AMPS/D-AMPS/IS-95; or INHAP for PDC. In the IS-41 specification, for example, inter-exchange transfer is specified for call related signal quality measurements on specified channels. The signal quality measurements is done by a base station controlled from a second exchange, and transferred to a first exchange where the call for a mobile station is controlled. The measurements are carried out only for a specific mobile station and are used for obtaining a list of possible handover cell candidates for the specific mobile station from the second exchange. In this regard, see also International Application Number PCT/US94/12419 (International Publication Number WO 95/15665).
In the particular situation shown in FIG. 1A, the Source RNC 22.sub.1 has control of the connection with mobile station MS over legs 28.sub.1,3 and 28.sub.2,1. In order to set up the connection involving leg 28.sub.2,1, RNC 22.sub.1 previously requested radio sources from Target RNC 22.sub.2. After the radio resources have been requested from Target RNC 22.sub.2 and allocated by Target RNC 22.sub.2 to Source RNC 22.sub.1, there is no means for Target RNC 22.sub.2 to inform Source RNC 22.sub.1 that congestion is occurring in the radio network area managed by Target RNC 22.sub.2, e.g., a cell in which base station BS 26.sub.2,1 is situated. Thus, the Target RNC 22.sub.2 is not able to comprehensively manage or control congestion in the network region which it manages, in view of allocation of resources to Source RNC 22.sub.1 for connections controlled by Source RNC 22.sub.1.
A typical method for congestion control is based on a total power (e.g., interference) determination performed by a base station to which a call is about to be set up. The total power determination involves summing the power received from all mobile stations with which the base station is currently in communication. If the received power does not exceed a threshold, calls are continued. However, if the threshold is exceeded, the connections need to be reconfigured (e.g., change the allowed usage of resources by a connection, queue the connection, terminate the connection, or move the connection).
What is needed therefore, and an object of the invention, is a congestion control technique for managing congestion in a region of a network in which radio resources are utilized by a node in another region of the network.